White light generating LEDs, “white LEDs”, are a relatively recent innovation and offer the potential for a whole new generation of energy efficient lighting systems to come into existence. It is predicted that white LEDs could replace filament (incandescent), fluorescent and compact fluorescent light sources due to their long operating lifetimes, potentially many 100,000 of hours, and their high efficiency in terms of low power consumption. It was not until LEDs emitting in the blue/ultraviolet part of the electromagnetic spectrum were developed that it became practical to develop white light sources based on LEDs. As taught, for example in U.S. Pat. No. 5,998,925, white LEDs include one or more phosphor materials, that is photoluminescence materials, which absorb a portion of the radiation emitted by the LED and re-emit radiation of a different color (wavelength). Typically, the LED die generates blue light and the phosphor(s) absorbs a percentage of the blue light and emits yellow light or a combination of green and red light, green and yellow light or yellow and red light. The portion of the blue light generated by the LED that is not absorbed by the phosphor is combined with the light emitted by the phosphor to provide light which appears to the human eye as being nearly white in color.
Due to their long operating life expectancy (>50,000 hours) and high luminous efficacy (70 lumens per watt and higher) high brightness white LEDs are increasingly being used to replace conventional fluorescent, compact fluorescent and incandescent light sources.
Typically in white LEDs the phosphor material is mixed with a light transmissive material such as a silicone or epoxy material and the mixture applied to the light emitting surface of the LED die. It is also known to provide the phosphor material as a layer on, or incorporate the phosphor material within, an optical component (a photoluminescence wavelength conversion component) that is located remote to the LED die (typically physically spatially separated from the LED die). Such arrangements are termed “remote phosphor” arrangements. Advantages of a remotely located phosphor wavelength conversion component are a reduced likelihood of thermal degradation of the phosphor materials and a more consistent color of generated light.
Traditional incandescent light bulbs are inefficient and have life time issues. LED-based technology is moving to replace traditional bulbs and even CFL (Compact Fluorescent Lamp) with a more efficient and longer life lighting solution. However the known LED-based lamps have difficulty matching the omnidirectional (evenly in all directions) emission characteristics of an incandescent bulb due to the intrinsically highly directional light emission characteristics of LEDs.
FIG. 1 shows a schematic partial sectional view of a known LED-based lamp (light bulb) 10 that utilizes a photoluminescence wavelength conversion component. The lamp 10 comprises a generally conical shaped thermally conductive body 12 and connector cap 14 mounted to the truncated apex of the body 12. The body 12 further comprises a conical shaped pedestal 16 extending from the base of the body 12 and one or more blue light emitting LEDs 18 mounted in thermal communication with the truncated apex of the pedestal 16. In order to generate white light the lamp 10 further comprises a photoluminescence wavelength conversion component 20 mounted to the pedestal and configured to enclose the LED(s) 18. As indicated in FIG. 1 the wavelength conversion component 20 comprises a spherical hollow shell and includes one or more phosphor materials to provide photoluminescence wavelength conversion of blue light generated by the LED(s). To give a diffuse light emission, and for aesthetic considerations, the lamp 10 further comprise a light transmissive envelope 22 which encloses the wavelength conversion component 20.
Whilst the lamp 10 of FIG. 1 has an improved emission characteristic, the emission characteristic of such a lamp fails to meet required industry standards since it emits too much light on axis 24. A further problem with such lamps is the relatively high manufacturing cost of the photoluminescence wavelength conversion component which is typically manufactured by injection molding. The high cost of manufacture results from the opening of the component being smaller than the maximum internal size of the component requiring use of a collapsible former to enable removal of the component from the injection molder. Embodiments of the invention at least in-part address the limitation of the known LED-based lamps.